Why do we use acids for heavy metal extraction?

When we are doing heavy metal extractions from plant samples we use acids like HNO3 or HCL .
I want to know what is the importance of these acids in extraction and I need to know about the mechanism of the action of the acids.


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  • Rahul Maurya · Central Salt and Marine Chemicals Research Institute
    Most of the metals by acid extraction... form either M nitrate, M sulfate or M phosphate..... That will detect by ICP analysis... in which different metal nitrates are used for standards..........
  • Carlos Garcia-Delgado · Universidad Autónoma de Madrid
    The objectives of acid digestion are: attack the matrix where these metals are embedded and solubilize heavy metals. Therefore, the acids must be oxidizer and/or present complex properties and not precipitate analytes (H2SO4 and Pb).
  • Dan Short · Robert Morris University
    Principles of Acid Digestion and Selection of Acid

    (i) HNO3 acts as both acid and oxidizing agent

    As acid it dissolves inorganic oxides

    CaO + 2H3O+ → Ca2+ + 3H2O

    As oxidizing agent HNO3 can oxidize zero valence inorganic metals and non-metals into ions

    Fe + 3H3O+ + 3HNO3 → Fe3+ + 3NO2 + 6H2O
    3Cu + 6H3O+ + 2HNO3 → 2NO + 3Cu2+ + 10 H2O

    (ii) HNO3 does not form any insoluble compounds with metals and nonmetals, whereas H2SO4 and HCl do

    Zhang, C. (2008) Fundamentals of Sampling and Analysis. Wiley.
  • Vishv Kumar · University of Allahabad
    Amino acid is highely found in plant, source of growth regulater and many toxic heavy metal found in acidic solution . then we are analysis in HCl extracts and convert in easy oxidizing complex.
  • Jerzy Mierzwa · Tennessee State University
    Basically, it is not only "heavy metal extraction", but the sample digestion/dissolution problem.
  • Bo Gao · China Institute of Water Resources and Hydropower Research
    H3O +HF can be used to digestion of soil and sediments.
  • Rizal Awaludin · Universitas Pendidikan Indonesia
    correct me if i'm wrong , as i know the HCl and HNO3 acid used to make the heavy metals "visible" when used on spectrophotometer
  • Mehjabeen Javed · Aligarh Muslim University
    I agree with my colleagues. Basically acid is used to release metal from matrix and make available in water for easy and accurate analysis .
  • Yogesh Patil · Symbiosis Institute of Research & Innovation (SIRI), Symbiosis International University
    Heavy metals present in any of the materials like plants, soils, solid waste can be extracted or leached using strong or weak acid and it also depends upon the solubility of the respective metal. In general, metals are in soluble in acids (HCl, H2SO4, HNO3, etc,). Like for example, Cu can be extracted using acid (say H2SO4) and will form of copper sulphate. However, this will happen only when the pH of the acid solution is less than 5.5. This is true for most of the metals like zinc, nickel, lead, cadmium, iron,etc. In the presence of alkali, metals in solutions tends to precipitate.
    Cu + 2OH- -------> Cu(OH)2 (ppt)
    Also metals in solution can only be detected or analysed from aqueous solution when the pH of solution is acidic.
  • Rachna Chandra · Tamil Nadu Agricultural University
    acid is used to release the metal available to be determined. Moreover, acidic environment helps detect the metals.
  • Otitoju Olawale · Federal University Wukari
    Most heavy metals exist in combination of other organic materials in soil or plant matter, therefore acid help in breaking existing bonds between the metals and the matrix in which they are to be extracted from. Most metals however require acid digestion for solubility purpose.
  • Craig Smeaton · University of St Andrews
    The acid is used to release the metals from the matrix allowing it to be analysed. For contaminated land work the acid is used to dissolve the soil only leaving the contaminates which will most likely be metals.
  • Aminul Islam · Aligarh Muslim University
    Acids are used to digest the sample. For SELECTIVE and EFFICIENT metal extraction one need to perform multiple metal-chelate or ion-pair extraction.
  • Peter Schaefer · Independent Researcher
    Thank you
  • Supratim Biswas · Jadavpur University
    The concept behind using acid (weak or small) lies in the fact that it helps in converting the metal in their water soluble form thereby making it come into solution. This phenomenun is called leaching. Likewise water as well as alkali leaching is also practiced.

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